Using print statements will work with a MPI program, as the output from all processes is sent back to the console. However, it can be hard to sort out the output from different processes. Using the -l option with mpiexec will tag each output line with the process number that it came from. See the example below.
[amit@node05 PBS ~/cs430/lab/MPI/parallel-sum]:mpiexec -n 4 spmd_sum_3 1000000 I got 250000 from 0 Sending partial sum back: 250000 Sending partial sum back: 250000 Sending partial sum back: 250000 I got 250000 from 3 I got 250000 from 2 I got 250000 from 1 The total is 1000000. Time taken = 0.001284 seconds [amit@node05 PBS ~/cs430/lab/MPI/parallel-sum]:mpiexec -l -n 4 spmd_sum_3 1000000 [2] Sending partial sum back: 250000 [3] Sending partial sum back: 250000 [1] Sending partial sum back: 250000 [0] I got 250000 from 0 [0] I got 250000 from 2 [0] I got 250000 from 3 [0] I got 250000 from 1 [0] The total is 1000000. Time taken = 0.000842 seconds [amit@node05 PBS ~/cs430/lab/MPI/parallel-sum]: